Australian researchers released an audio recording Wednesday of an underwater sound that they say could possibly be related to the final moments of missing Malaysia Airlines Flight 370.
It's a long shot, but researchers at Curtin University near Perth, Australia, have been studying records from underwater listening devices, including those meant to monitor for signs of underwater nuclear explosions, in an effort to help find the missing plane.
"One signal has been detected on several receivers that could be related to the crash," said Alec Duncan with the university's Centre for Marine Science and Technology (CMST).
Researchers have been analyzing the very low frequency sound for weeks to see if it was "the impact of the aircraft on the water or the implosion of parts of the aircraft as it sank," Duncan said. "But (the source of the noise) is just as likely to be a natural event."
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The Department of Homeland Security has pared the number of Federal Air Marshals - plain-clothed officers whose job is to protect aircraft from terrorists - during the past three years, according to an internal email obtained by CNN.
Budget cuts have "led to ... a reduction in FAMs (Federal Air Marshals) through attrition," the email said.
The exact number of marshals is secret, and the Homeland Security Department on Tuesday declined to say how positions have been eliminated. Nor would it say what percentage of marshals positions were cut.
But critics, including some air marshals, say the secrecy allows the government to cut the workforce without acknowledging it, as happened in the years leading up to the September 11, 2001, terrorist attacks.
At that time, fewer than 40 people were in the air marshal workforce and none were on the hijacked planes.
Following the attacks, DHS assumed responsibility for the program and ramped up its ranks on domestic and international flights serving the United States.
Their numbers grew exponentially and although the figure is confidential, the agency two years ago negotiated pay disputes with some 3,500 air marshals - a number believed to represent the bulk of the workforce.
Air Marshal Director Robert Bray said in an e-mail, sent Friday, that the agency's budget has been cut from $966 million to $805 million in the past three years. He outlined plans to close six of the agency's 26 field offices in coming years.
San Diego and Tampa will close by the end of 2014, followed by Pittsburgh and Phoenix, by June 2015, and Cleveland and Cincinnati by June 2016, the email says.
In addition, the agency has frozen hiring at three other offices: Las Vegas, Seattle, and Denver, the email says.
Existing personnel will be reassigned to other offices, and the closures "will not adversely impact our ability to maintain coverage onboard flights at the corresponding airports," Bray wrote.
Jon Adler, president of the Federal Law Enforcement Officers Association, noted the drop-off.
"There's definitely been attrition, but not from the natural progression of a 20-year retirement," said
Adler, president of the Federal Law Enforcement Officers Association, which includes air marshals. "'Attrition' is really a euphemism for 'exodus,'" Adler said.
Air marshals complain the agency suffered from mismanagement, particularly in the early years of the program.
Two years ago, the DHS Inspector General concluded that agency supervisors did not engage in "widespread" discrimination, but that air marshals shared a widespread "perception" that they were being mistreated.
It also said that investigators "heard too many negative and conflicting accounts" of misconduct to dismiss them.
"Federal air marshals repeatedly portrayed their supervisors as vindictive, aggressive, and guilty of favoritism," the report said. "There is a great deal of tension, mistrust and dislike."
In his email, Bray said the consolidation of field offices is being done after considering mission scheduling, current threat reporting and trends in airline scheduling.
But Adler said he believes DHS is counting on the consolidation of field offices to further thin the ranks.
"There has to be a realistic expectation that the numbers are going to decrease," he said.
Mike Karn, president of the Coalition of Airline Pilots Associations, said it was not wise to cut those positions.
"Diminishing any level of security that we have out there right now concerns me," Karn said.
A company dispatcher who was seated in the cockpit jump seat as Southwest Airlines Flight 4013 landed at the wrong Missouri airport has been placed on paid leave pending the outcome of the investigation, the company told CNN on Tuesday.
Investigators will want to know whether the dispatcher distracted the pilot as the Boeing 737 and its 124 passengers approached the airport, a source familiar with the investigation told CNN.
The pilots of Sunday's flight, which departed from Chicago's Midway airport, remain on paid leave.
The dispatcher will give investigators another source of information and open up another line of questions surrounding the landing at M. Graham Clark Downtown Airport near the resort community of Branson, Missouri.
An industry official said the Federal Aviation Administration, which is conducting its own investigation, has reviewed the actions of air traffic controllers at Branson Airport and "indicate that there appears to be no controller issue."
The Southwest dispatcher was authorized by the company to fly in the jump seat - which is a fold-down seat in the cockpit.
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It is undoubtedly hard to imagine the pilot flying the plane you're on may not fully understand how the automated flight systems in the cockpit work.
"It's disturbing and that's what new details in the Asiana crash suggest," reports CNN's Rene Marsh.
The pilot of an Asiana Airlines jet that crashed in San Francisco this year told investigators after the accident that he had been "very concerned" about landing without help from an airport navigation system that was out of order.
Capt. Lee Kang Kuk, who was highly experienced in a Boeing 747 but was transitioning to flying a 777, told the National Transportation Safety Board that he found it "very stressful, very difficult" to land without the glideslope indicator that helps pilots determine whether the plane is too high or too low during approach.
"Asked whether he was concerned about his ability to perform the visual approach while piloting Asiana Flight 214, he said 'very concerned, yea,'" the safety board revealed at a hearing on Wednesday on its investigation into the July 6 crash that killed three people and injured more than 180 others.
The jet struck a sea wall and broke apart on the runway following a missed approach.
The navigation aid that syncs up with aircraft instruments was out of service while the Capt. Lee Kang Kuk made runway safety improvements. But a second, visual lighting system was operable at the time of the daytime crash and the weather was clear.
The safety board investigation is focusing on whether pilots have become overly reliant on automation to fly commercial planes, and whether basic manual flying skills have eroded.
Investigators have also focused on the pilot understanding - or misunderstanding - of the plane's auto-thrust system, which controls aircraft power.